In the field of the photographic industry notably, films are cut to size (35 mm, 16 mm) from a wide sheet (typically 1.30 m wide) which is cut along the length so as to form a plurality of strips of relatively low width. The strips thus formed are wound onto spindles disposed on a motorized winding cantilevered shaft. When a sufficient length of film has been wound onto the spindles, the rolls are unloaded from the winding shaft for a new winding cycle. Generally, this operation is carried out in hidden time, using two winding shafts, one of the shafts being unloaded while the strips are being wound onto the other, thereby limiting as much as possible the stoppage time for the film cutting machine.
In general terms, the rolls are transferred from the winding shaft to an unloading shaft, from which the rolls are unloaded onto cradles provided for this purpose. Typically, transfer from one shaft to the other is carried out by means of a pushing device which surrounds the winding shaft and which is controlled so as to move in translation along the shaft, driving the rolls towards the free end of the shaft.
One of the main problems associated with this roll unloading operation relates to the alignment of the winding shaft and unloading shaft, which is a vital condition for the transfer of rolls by means of pushing. This is because, when it is loaded, the end of the winding shaft flexes under the weight of the rolls, so that it is situated at a height substantially lower than the free end of the unloading shaft designed to receive the rolls (typically, this difference in height can be as much as 1 cm). Such a difference is quite enough to prevent the unloading of the rolls by pushing.
Conventionally, such shafts were aligned by disposing a cone forming a projection on the section of the free end of one of the shafts, a conical recess being formed on the end section of the other shaft so as to receive the said cone. Thus, during the positioning of the unloading shaft with respect to the winding shaft, the cone is engaged in the conical recess, thus compensating for the differences in height between the two shafts. The major drawback with this approach relates to the fact that, when there is a large difference in alignment, the conicity required is large, leading to significant friction, necessitating a substantial amount of energy to bring the two shafts into alignment. This high level of friction also leads to a rapid wearing of the surfaces of the cone and/or of the recess, which inevitably leads to a reduction in the precision of positioning. Furthermore, the cone is in abutment against the walls of the conical recess, thus limiting the depth of engagement between the two shafts. Thus, during the transfer of the rolls from one shaft to the other, the cone can be disengaged from the recess; the winding shaft is then no longer aligned with the unloading shaft, which leads to an interruption in the unloading process.
The problem of the alignment of one component with respect to another also presents itself for applications other than the one referred to previously. By way of example, the handling of objects by robots might be cited, one difficulty with which relates to the fact that the robot must pick up components whose position is known only approximately and which must be transported to a precise location. Typically, this problem is resolved either by improving the precision of the positioning of the component to be gripped, or by equipping the robot with an electronic vision and image analysis system. This approach is costly and increases the cycle time of the robot, owing principally to the time required for the image analysis.